Healthy foods can be hard to find in poor neighborhoods. To address the problem, some recently introduced programs in the United States use loans and grants to boost the number of local grocery stores in these areas. However, the effectiveness of these programs in improving diet and reducing obesity has not been closely examined.

In the new study, researchers from Penn State University and the London School of Hygiene and Tropical Medicine assessed the impact of a new supermarket that opened in a poor neighborhood in Philadelphia. The store was one of 88 new or expanded food retail outlets opened in the area under the Pennsylvania Fresh Food Financing Initiative.

Researchers followed 650 neighborhood residents for four years and found that they didn't make significant changes to their diets despite being aware that healthier foods were available.

Only 27 percent of the residents used the new supermarket as their main food store, and only 51 percent used the store at all. The supermarket's presence had little effect on the residents' fruit and vegetable intakes or obesity rates, according to the study, which was published in the February issue of the journal Health Affairs.

The findings are similar to those of previous studies in the United Kingdom, the researchers said.

"Though these interventions are plausible and well-meaning, this study suggests that they are only effective in taking us part of the way in changing dietary behavior," study lead author Steven Cummins, a professor of population health at the London School of Hygiene and Tropical Medicine, said in a school news release. "In order to realize their full potential we need to better understand how to translate changes in perception to changes in behavior."

Increasing the number of grocery stores in poor neighborhoods needs to be accompanied by sales and marketing to encourage residents to use these stores, the researchers said.